Fluid pressure variations in a vehicle brake system may cause the amount of brake torque or brake pressure requested by the driver to differ from that actually experienced out at the vehicle wheel or corner. There are a variety of potential sources of fluid pressure variations, including those that result in more fluid pressure than that requested by the driver and those that result in less fluid pressure than requested.
Hydraulic gain or amplification is an example of a source that may result in too much fluid pressure; that is, a vehicle brake system that uses hydraulic gain to boost the fluid pressure can provide more brake torque or brake force at the wheel than requested at the brake pedal. Conversely, frictional loss, which may occur in a master cylinder, actuator, valve, etc., is an example of a source that may cause the fluid pressure at the wheel to be less than that requested at the brake pedal. If the fluid pressure variations are significant enough, they may become noticeable to the driver.